1. Field of the Invention
This invention relates to an exposing aperture device for controlling exposure by moving diaphragms in a video camera and so on, and more particular to a structure capable of warranting high accurate exposing operation of the elements constituting an exposing aperture without being affected by undesirable factors such as burrs and molding flashes which are inevitably formed on a base plate for supporting the diaphragms as a result of making the base plate by a punching or molding process.
2. Description of the Prior Art
In general, an exposing aperture device for controlling exposure in a video camera and so forth, which is usually incorporated between lenses arranged along an optical axis in a lens tube and an image pick-up means such as a CCD image sensor, has a pair of exposing diaphragms movable in opposite directions relative to an exposing aperture formed around the optical axis in order to adjust quantity of light passing through the aperture.
As recent video cameras have come to enjoy remarkably improved properties, the exposing aperture devices incorporated in the video cameras are required to not only form an apposite aperture with a high accuracy, but also perform stable and smooth exposing operation instantaneously in response to the change of the quantity of light from a subject. Thus, the exposing diaphragms are desired to be made light and small in inertial mass and work accurately so as not to involve undesirable factors affecting the movement of the diaphragms.
In Japanese Patent Application Public Disclosures Nos. HEI 3-31831(A), HEI 3-145630(A), and HEI 7-295028(A), and Japanese Utility Model Appln. Public Discl. Nos. SHO 59-4524(A), and HEI 7-41532(A), exposing aperture devices of this type are disclosed.
The conventional exposing aperture device for use in a video camera, as typically disclosed in Japanese Utility Model Appln. Pub. Disclosure No. SHO 59-4524(A), comprises a base plate having an exposing aperture formed around the optical axis and pin-like diaphragm guide members, a pair of exposing diaphragms having guide slots which receive the guide members so as to be movable in opposite directions away from the exposing aperture, and a drive means for moving the exposing diaphragms.
The parallel movement of the diaphragms is ensured by a guiding structure composed of the guide members planted on the base plate and the guide slots or grooves formed in the diaphragms. By the guiding structure, the diaphragms can be stably moved to and fro relative to the exposing aperture without wobbling nor snaking.
The guiding structure in which the guide members such as pins are inserted into the guide slots as found in the aforementioned conventional exposing aperture device enjoys high operating performance and proves advantageous from the standpoint of a space factor in comparison with an aperture device disclosed in Japanese Patent Appln. Pub. Disclosure No. HEI 8-19239(A), in which the diaphragms are held between outside guide members.
The base plate is provided on its surface confronting the diaphragm with one or more longitudinal ribs so as to come into contact with the diaphragm as little as possible, thus to heighten the moving efficiency of the diaphragm.
In most cases, the base plate is generally produced by a punching method, a resin molding method or the like. In case where the base plate is punched out of sheet metal by using a punching press, serrate shaped burrs are inevitably left on the sheared edge of the base plate. The film-like light and thin diaphragm is caught and sensitively affected by the burrs on the edge of the base plate to no small extent when moving on the base plate, consequently to degrade the exposing accuracy of the camera. The base plate produced by the resin molding method might lead to the same problem.
To solve the matter, the burrs resulting from punching or molding may be removed by hand, but such a onerous handwork to remove the burrs consumes much time and labor and entails a decline in productivity of the exposing aperture device. Under these circumstances, there has been a great need for a high-performance aperture device in a field of optics, which can easily produced and stably and accurately operate without being affected by undesirable factors such as the burrs inevitably left on the base plate.